Abstract: To improve the solution searching efficiency of NSGA-Ⅱ in the multi-objective optimization of water quality monitoring station, an external archive is established to store non-dominant solution and the option of the paternal chromosomes improved on the basis of NSGA-Ⅱ. NSGA-Ⅱand improved NSGA-Ⅱare respectively used to solve the multi-objective optimal placement of water quality monitoring station in example network. The result shows that: comparing with NSGA-Ⅱ, the improved NSGA-Ⅱsaves about 42% of the operation time and improves the efficiency of solving in the complete non-dominant optimal solution. The improved NSGA-Ⅱis more applicable to solve multi-objective optimal placement of water quality monitoring station in actual network.